Conventionally, what is shown in FIGS. 19-20 is known as the mounting structure for IC chips, and lead frame material 1 shown in FIG. 21 is used in the mounting.
The lead frame material 1 is formed entirely of metal (e.g., 42 alloy, copper alloy, copper, etc.), and lead frame outer frame 2 and lead frame part 8 having a plurality of inner leads 7 extending radially in four directions in the inside position are formed as one body by etching, etc.
Namely, in lead frame part 8, outer leads 6 are connected by linear connection parts (dumb bar) 9 at each side and the connection parts are integrated to outer frame 2 with each corner part of lead frame part 8.
IC chip 10 is mounted on a square shaped mounting pad (die pad) 11 having a larger area than the area of IC chip 10. Support pins 12 which support the mounting pad 11 are provided on the mounting pad 11 and are integrated with outer frame 2 at the corner parts. 4 in the figure is the hole for positioning the lead frame material.
Semiconductor package 13, which is fixed, wire bonded, and resin-sealed as shown in FIGS. 22-24 using the lead frame material 1, is mounted (fixed) with silver paste 14 on mounting pad 11 as shown in FIGS. 19-21. Pad 17 is bonded to inner lead 7 with wire 15, and structured to be totally sealed with resin 16 such as epoxy, etc. In FIG. 20, the alternating long and short dashed line indicates the outer line of sealing resin 16 and alternating long and two short-dashed line indicates the position of IC chip 10.
When manufacturing the package 13, IC chip 10 is mounted with silver paste 14 on mounting pad 11 as shown in the enlarged figure of FIG. 22.
Next, heater member (heater insert or heater block) 18 is contacted to mounting pad 11 from the bottom side during the wire bonding as shown in FIG. 23 so that heat of the heater is conducted to the bonding pad (pad 17) simultaneous with supporting mounting pad 11.
Wire bonding is executed by coupling wire 15 to bonding pad 17 with capillary 19 while providing thermal and ultrasonic energy, guiding it to inner lead 7 as indicated by arrow 20, then cladding it.
As noted above, in the conventional package structure, mounting pad 11 of IC chip 10 was formed to be larger than IC chip 10, but this was mainly due to the following reasons.
First of all, if mounting pad 11 is made smaller than IC chip 10 as shown in FIG. 24 during the bonding, the peripheral part of mounting pad 11 does not contact heater insert 18, so IC chip 10 slants during the ultrasonic function based on capillary 19, the support becomes unstable, ultrasonic energy cannot be used effectively, and the heat from heater insert 18 is not conducted efficiently to IC chip 10. Thus imperfect bonding is executed. Therefore, making the mounting pad 11 smaller than IC chip 10 was considered by those in the industry to be impractical and undesirable.
Also, when soldering resin sealed package 13 to a circuit pattern 22 on a printed circuit board 21 as shown in FIGS. 25 or FIG. 26, solder 23 is fused by solder reflow (e.g., IR reflow by infrared irradiation) then solidified, but cracks 24 may be created in resin 16 as shown in the figures.
If the overall thickness of package 13 is sufficient, the cracks 24 are not created, but when thinning and enlargement in the chip are required as in recent years, separation part 25 is easily created at the boundary of resin 16 in the mounting pad 11 as shown in FIG. 25, and the phenomenon of cracks 24 being created from edge 11a of pad 11 has been observed from time to time.
This is due to the peripheral water vapor preserved by the package being sucked into the hold resin, the water vapor condensing and becoming water between the lead frame and the resin, the water converting to water vapor during the IR reflow, which suddenly expands causing so-called vapor explosion, resulting in the peeling off of the resin from the lead frame.
Assisting in causing the phenomenon of the cracks in the resin, curvature is created and the package itself is deformed due to warpage remaining on the inside of the package after the completion of resin molding and setting due to differences in the thermal expansion coefficient of the mounting pad, IC chip, and resin.
Also, as another cause for the cracks, it is a fact that silver paste 14 for fixing IC chip 10 is a material with very high hygroscopicity, such that the hygroscopic moisture may cause vapor explosion during the heating such as IR reflow, etc.
Namely, as shown in FIG. 26, pad 11 is deformed by the condensed water causing vapor explosion due to a phenomenon similar to the above-mentioned in the part with silver paste 14, great stress is applied to resin 16, and cracks 24 are created in particular from edge 11a of pad 11.
It is an object of the present invention to provide a semiconductor device package in which the generation of warpage and cracks in the sealing resin and the lead frame thereof is noticeably reduced or prevented.
It is another object of the present invention to provide a method of making a semiconductor device package, wherein the bonding of the semiconductor element and leads can be achieved efficiently and stably.